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Mechanisms of solute efflux from seed coats: whole-cell K+ currents in transfer cell protoplasts derived from coats of developing seeds of Vicia faba L



Mechanisms of solute efflux from seed coats: whole-cell K+ currents in transfer cell protoplasts derived from coats of developing seeds of Vicia faba L



Journal of Experimental Botany 48(313): 1565-1572



In developing seed of Vicia faba L., solutes imported through the phloem of the coats move symplastically from the sieve elements to a specialized set of cells (the thin-walled parenchyma transfer cells) for release to the seed apoplast. Potassium (K+) is the predominant cation released from the seed coats. To elucidate the mechanisms of K+ efflux from seed coat to seed apoplast, whole-cell currents across the plasma membranes of protoplasts of thin-walled parenchyma transfer cells were measured using the whole-cell patch-clamp technique. Membrane depolarization elicited a time-dependent and an instantaneous outward current. The reversal potential (E(R)) of the time-dependent outward current was close to the potassium equilibrium potential (E(K)) and it shifted in the same direction as E(K) upon changing the external K+ concentration, indicating that this current was largely carried by an efflux of K+. The activation of the time-dependent outward K+ current could be well fitted by two exponential components plus a constant. The instantaneous outward current could also be carried by K+ efflux as suggested by ion substitution experiments. These K+ outward rectifier currents elicited by membrane depolarization are probably too small to represent the mechanism for the normal K+ efflux from seed coat cells. Membrane hyperpolarization more negative than -80 mV activated a time-dependent inward current. K+ influx was responsible for the inward current as the current reversed at membrane voltage close to E(K) and shifted in the same direction as E(K) when external [K+] was varied. Activation of this K+ inward rectifier current was well fitted with two exponential components plus a constant. A regulating function for this current is suggested.

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Accession: 002892669

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DOI: 10.1093/jxb/48.8.1565


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